The success of targeting signal transduction pathways for the development of new prostate cancer therapies has been limited to date by the subsequent development of drug resistance mechanisms. Highly activated AKT protein kinase found in almost 70% of cases of metastatic prostate cancer are an important target for therapies in this disease. Preliminary data in this proposal demonstrate that the addition of AKT inhibitors to prostate cancer cell lines induces a marked increase in cell surface receptor tyrosine kinases (RTKs) that function to limit the activity of these inhibitors in part by elevating ERK activity. Importantly, it is also demonstrated that AKT inhibitors induce the Pim-1 protein kinase, an enzyme that has been implicated in prostate cancer initiation and progression. This research team has discovered that knocking down Pim-1 either by siRNA or in genetically engineering mouse fibroblasts will inhibit the feedback in which AKT inhibitors induce RTKs. Using a small molecule Pim-1 inhibitor developed by the Kraft laboratory team, they have demonstrated that the combination of an AKT and Pim-1 inhibitor synergistically blocks prostate cancer cell growth in tissue culture, and markedly inhibits the growth of tumors in immunosuppressed animals. Data obtained suggests that AKT and Pim inhibitors regulate the translation of RTKs. These exciting findings lead to the unique hypothesis that AKT inhibitor treatment causes a Pim-1-directed feedback loop that induces RTKs that in turn stimulates increases in ERK activity. Thus, the combination of an AKT and Pim inhibitor will interrupt the induction of Pim-1 and synergize to kill prostate cancer. The specific aims in this proposal are to explore and validate this hypothesis by: 1) demonstrating in complex cell culture and animal models of prostate cancer that knocking down Pim-1 activity enhances AKT inhibitor tumor killing; 2) deciphering how AKT inhibitors increase the Pim-1 protein kinase and modulate translation to increase RTK levels; and 3) exploring how these agents can be best combined for tumor killing and to inhibit metastatic cancer, and examining whether the combination of AKT and Pim inhibitors induces a marked increase in reactive oxygen species (ROS) in prostate tumors. These studies will identify RTKs, phosphorylated ERK, and Pim-1 levels as potentially clinically important intermediate markers of AKT inhibitor action. The proposed study designs will make use of unique genetically engineered mouse models, and ribosome profiling and foot printing to explore these questions. When completed, these studies will focus attention on the potential for the development of combination therapies with Pim and AKT inhibitors to target feedback resistance mechanisms. This combination would markedly enhance responses to single agent therapies currently under investigation for the treatment of prostate cancer.